1. Field of the Invention
This invention relates to a vibrating driven motor (an oscillatory-wave-motor).
2. Description of the Related Art
For a long time the assignee of the present application has practically utilized a vibration driven motor (an oscillatory-wave-motor), in which surface-acoustic-wave vibration is generated on the surface of a vibrator, by piezoelectric elements and the like, and vibrational energy of the vibrator is converted into a continuous mechanical movement. The vibration driven motor has been used a driving motor for an optical apparatus, such as a camera or the like. Various kinds of vibration driven motors have different power-generation principles and mechanical structures, and various kinds of vibration driven motors have been developed and practically utilized by the assignee of the present application.
A description will now be provided of a bar-shaped vibrating motor developed by the assignee of the present application and mounted in a conventional optical apparatus relating to the present invention.
FIGS. 9 and 10 illustrate the mechanical structure and the electrical configuration of the bar-shaped vibration driven motor, respectively.
In FIG. 9, vibrator 101 of the vibration driven motor is formed by inserting groups of circular piezoelectric elements, serving as electromechanical energy transducers, in intermediate portions of the main body of the vibrator 101, comprising a thick metallic cylindrical member. By applying AC voltages having different phases to the respective groups of piezoelectric elements, local elliptical vibration is generated at a distal-end surface of the vibrator 101. The piezoelectric elements inserted in the main body of the vibrator 101 comprise a group of A-phase piezoelectric elements and a group of B-phase piezoelectric elements to which a first voltage and a second voltage are applied, respectively, in order to generate the elliptical vibration at the distal-end portion of the vibrator 101, and a group of piezoelectric elements S, serving as mechanoelectrical energy transducers, for detecting the state of vibration of the vibrator 101.
A rotating member (rotor) 102 is rotated by the surface-acoustic-wave vibration at a distal-end surface of the vibrator 101 by being subjected to pressure contact therewith. An output gear 103 is connected to the rotating member 102.
Since the principle of operation of such a vibration driven motor has been disclosed, for example, in Japanese Patent Laid-Open Application (Kokai) No. 3-289375 (1991), a description thereof will be omitted.
The group of A-phase piezoelectric elements comprises two piezoelectric elements a1 and a2, the group of B-phase piezoelectric elements comprises two piezoelectric elements b1 and b2, and the group of piezoelectric elements S for detecting vibration comprises a single piezoelectric element s.
A grounding electrode GND-d is in tight contact with the outer surface of the piezoelectric element a1. A driving electrode A-d for applying the first AC voltage for driving is inserted between the piezoelectric elements a1 and a2. A grounding electrode GND-d is inserted between the piezoelectric elements a2 and b1. A driving electrode B-d for applying the second AC voltage for driving is inserted between the piezoelectric elements b1 and b2. A grounding electrode GND-d is inserted between the piezoelectric elements b2 and s. An electrode S-d for detecting vibration is in tight contact with the outer surface of the piezoelectric elements.
That is, each of the two pairs of piezoelectric elements, a1 and a2, and b1 and b2 is inserted between the grounding electrodes GND-d. An A-phase driving signal (to be described later) is applied to the piezoelectric elements a1 and a2 via the driving electrode A-d present therebetween, and a B-phase driving signal (to be described later) is applied to the piezoelectric elements b1 and b2 by the driving electrode B-d present therebetween. The vibration of the piezoelectric element s is detected by the electrode S-d for detecting vibration. As shown in FIG. 9, an insulating sheet 104 is attached to the-other distal-end surface of the main body of the vibrator 101 in order to prevent the electrode S-d from being electrically grounded.
FIG. 10 illustrates the schematic configuration of driving control means for applying AC voltages, serving as driving signals, to the A-phase piezoelectric elements a1 and a2 and the B-phase piezoelectric elements b1 and b2.
In FIG. 10, a microprocessor 11 constitutes frequency control means for setting and changing the frequency of the AC voltages to be applied to the group of A-phase piezoelectric elements (in FIG. 10, the piezoelectric elements a1 and a2 are represented by a single element) and the group of B-phase piezoelectric elements (in FIG. 10, the piezoelectric elements b1 and b2 are represented by a single element). An oscillator 2 is a known voltage controlled oscillator (VCO) or the like for generating an AC signal having a frequency corresponding to an instruction signal generated from the microprocessor 11. Reference numeral 3 represents a known phase shifter for shifting the phase of the output signal of the oscillator 2 by a predetermined amount (for example, 90 degrees). Switching circuits 4 and 5 comprise, for example, push-pull amplifying circuits for amplifying the outputs of the oscillator 2 and the phase shifter 3 by switching the voltage of a high-voltage power supply with the output of the oscillator 2 and the phase shifter 3, respectively. Matching coils 6 and 7 match the impedance of the driving control means side with the impedance of the vibrator side. A phase-difference detector 10 detects the difference between the phase of a voltage signal generated by the piezoelectric element s for detecting vibration and the phase of the A-phase driving signal applied to the A-phase piezoelectric elements.
The driving control means, including the microprocessor 11 and the other above-described circuits, drives the vibration driven motor both when starting the vibrating motor and during a steady-state operation. The microprocessor 11 recieves the output of the phase-difference detector 10 and uses that information to control the frequency of the A-phase driving signal and the B-phase driving signal.